the Diviner |
Huge - Corpse Lotus (4 attacks with Grab plus Constrict)
Large - Strangle Reed (2 attacks with Grab plus Constrict)
If you buy an Anaconda's Coils then the medium sized Mi-Go becomes quite cool.
Medium - Mi-Go (4 attacks with Grab, fly, DR/Slash, Resistance to cold, electricity, and fire)
Note that all of these are plants. I had some notes on a plant based wild shape user lying around but there might be some good ones for animals as well. I expect some of the aquatic forms work well for this.